Rectifier protective system



July 12 1938. wlNOGRAD 2,123,859

RECTIFIER PROTECTIVE SYSTEM Original Fi ed F b.. 13, 1933 5 Sheets-Sheetl :mlym

July 12, 1938. H. WINOGRAD RECTIFIER PROTECTIVE SYSTEM Original FiledFeb. 13, 1933 5 Sheets-Sheet 2 H. WINOGRAD REC TIFIER PROTECTIVE SYSTEMJuly 12, 1938.

Original Filed Feb. 13, 1933 5 Sheets-Sheet 3 97 I /a/ m2 4 as I -93 931I I Y I l July 12, 1938. H. WINOGRAD 2,123,859

RECTIFIER PROTECTIVE SYSTEM Original Filed Feb. 13, 1933 5 Sheets-Sheet4 July 12, 1938. H. WINOGRAD v RECTIFIER PROTECTIVE SYSTEM OriginalFiled Feb. 13, 1935 5 Sheets-Sheet 5 Patented July 12, 1938 UNITEDSTATES PATENT OFFICE RECTIFIER PROTECTIVE SYSTEM Application February13, 1933, Serial No. 656,524 Renewed flctober l, 1937 15 Claims.

such failure being possible as a result of one or more of variousaccidental causes. An anode may fail to carry current because theconditions. of vapor pressure and temperature within the space betweensuch anode and the cathode are such that ionization is not suflicientlyreadily established in such space at the voltage appearing between theanode and the cathode. Such failures occur particularly easily inelectron discharge devices operating in parallel with other convertingequipment and also in electron discharge devices in which groups ofseveral electrodes are operated in parallel. In devices so connected,the potential of any anode generally becomes positive with respect tothe potential of the cathode by an amount which is only slightly greaterthan the value of the arc drop and which may therefore be insufficientfor ionizing the arc path under unfavorable conditions. When thefunctioning of the anodes is controlled by the action of controlelectrodes, the deterioration or failure of one of such controlelectrodes or a defect in the connection thereof may cause the anodeassociated with such control electrode to carry current prematurely,tardily or not at all during'each normal cycle of operation thereofdepending upon the nature of the deterioration and upon the method ofenergization of the control electrode. Some of the anodes of the devicemay also fail to be energized because of the failure of a phase in thesource supplying such device or in other apparatus included in thealternating current circuit. Such condition may arise, for instance,upon breakage of one of the alternating current conductors or uponfailure of one phase of a circu t breaker or as a result of an openconnection within the windings of a supply transformer.

The operation of an electron discharge device in which only part of theelectrodes carry current is highly detrimental to the safety of thedevice as the operative electrodes are more or less severely overloadedby such operation. All operative electrodes are then overloaded as theseveral phase voltages of the device must be increased to obtain thesame average output voltage as when all electrodes are functioning. In 5addition, the electrodes preceding and following the inoperativeelectrode during the normal cycle of operation thereof are even moreseverely overloaded as they must carry current over the period duringwhich the inoperative electrode is normally functioning. If a group ofseveral electrodes are operated in parallel on one phase of the device,the operative electrodes of the group must carry the current of theinoperative electrodes in addition to the current normally carried. Suchoverloads may result in a serious deterioration or even completedestruction of the electrodes, and may also result in the deteriorationof the associated transformer windings by overheating. In addition tothe detrimental results above mentioned, the circuits connected with thedevice then receive voltage and current components apt to causeinterference in communication circuits, train control circuits, etc. byelectromagnetic or electrostatic induction.

No indication of the failure of some of the electrodes is given by theusual type of ammeter and voltmeter inserted in the input or outputcircuit of the device as such meters only indicate the average values ofvoltages and currents. Such failure could be detected by insertingsuitable ammeters in the circuits of each main electrode and controlelectrode of the device. When the number of electrodes of the device islarge, the number of such ammeters becomes large and the installationbecomes complicated and excessive in cost. Such ammeters cannot be useddirectly to'control or to give an audible or visible signal or forcontrolling the disconnection of the device upon failure of one of theelectrodes to 40 function because such failure results in unequalammeter readings rather than in' any particular value of such readings.

A simpler, more dependable, and less expensive method consists inutilizing some of the voltage and current components which appear in thecircuits associated with the device and in the circuits of anyelectrode-paralleling device associated therewith, upon failure of oneor more electrodes to function, such components not being present whenall electrodes carry substantially equal amounts of current. Suchcomponents may thus be directly utilized for controlling thedisconnection of the device upon the appearance of the components andresonant filters may be used for segregating such components fromcurrent and voltage components of other frequencies which may be presentin the circuits under all conditions of operation and to which thecontrol and indicating system should not be responsive.

, It is accordingly among the objects of the present invention toprovide a protective system for electron discharge devices whereby theflow of current within such a device may beinterrupted or reduced uponfailure of one or more of the electrodes thereof to function in thenormal manner thereof.

Another object of the present invention is to provide a protectivesystemfor electron discharge devices whereby the flow of current within such adevice may be interrupted or reduced upon failure of one or more of theelectrodes thereof to carry current.

Another object of the present invention is to provide a protectivesystem for electron discharge devices whereby such a device may bedisconnected from the supply line or from the output line upon failureof one or more of the electrodes thereof to carry substantially the sameamount of current as is carried by other similarly connected electrodes.

. Another object of the present invention is to provide a protectivesystem for electron discharge devices wherebysuch a device may bedisconnected from the supply line or from the output line upon failureof. one or more of the electrodes thereof to carry substantially thesame amount of current as is carried by electrodes connected in paralleltherewith.

Another object of the present invention is to provide a protectivesystem for electron discharge deviceswhereby such a device may bedisconnected from the supply line or from the output line upon faultycontrolling operation of one or more of the control electrodes thereof.

Another object of the present invention is to provide a protectivesystem for electron discharge devices whereby such a device may bediscomnected. from the supply line or from the output line in responseto the appearance of current or voltage components occurring uponfailure of one or more of the electrodes thereof to function in thenormal manner.

Another object of the present invention is-tc provide a protectivesystem for electron discharge devices whereby such a device may bedisconnected from the supply 'line or from the output line, and in whichthe system is selectively responsive to sustained voltage or currentcomponents in a circuit connected with the device when such componentsare due to accidental or abnormal operation of the device.

Another object of the present invention is to provide a protectivesystem for electron discharge devices whereby such a devicemay bedisconnected from the supply line or from the output line, and in whichthe system is selectively respomive to the flow of sustained voltage orcurrent components accidentally appearing in the circuit of anelectrode-paralleling device.

Objects and advantages other than those above set forth will be apparentto those skilled in the art from the following description when read inconnection with the accompanying drawings in which:

Fig. l diagrammatically illustrates one embodiment of the presentinvention which comprises means selectivelyresponsive to componentsacci-. dentally appearing in the output direct current araaeae voltageof a six phase'electron discharge device operable as an alternatingcurrent rectifier, and is designed for the purpose of disconnecting suchdevice from the supply line thereof;

Fig. 2 is a diagram of the direct current output voltage of the deviceillustrated in Flg. l in which it is assumed that one anode and onecontrol.

electrode have become inoperative;

Fig. 3 diagrammatically illustrates another embodiment of the presentinvention in which the voltage responsive circuits of the system areenergized at voltages appearing at the terminals of an interphasetransformer associated with the main transformer secondary windingsupplying the electron discharge device, and are connected to cause themain current to be interrupted by the action of the control electrode ofthe device;

Fig. 4 diagrammatically illustrates a portion of a modified embodimentof. the present invention difiering from the embodiment illustrated inFig. 1 in that the voltage-responsive circuits of the system areenergized at voltages appearing in the circuit of the control electrodeenergizing means;

Fig. 5 diagrammatically. illustrates another embodiment of the presentinvention responsive to the flow of components accidentally appearing inthe direct current output line of the device to cause the main currentto be reduced or interrupted by the action of the control electrodes ofthe device.

Fig. 6 diagrammatically illustrates a portion of another modifiedembodiment of the present invention applied to the control of asix-phase 12anode electron discharge device operable as an alternatingcurrent rectifier, the control system operating in response to the flowof. current in the neutral connection between the secondary windings oftwo anode paralleling transformers;

Fig. 7 diagrammatically illustrates a portion of another modifiedembodiment of the present invention applied to the control of asix-phase 18-anode electron discharge device operable as an alternatingcurrent rectifier, the protective system operating in response to theappearance of residual current in the connection of the secondarywindings of three anode paralleling transformers;

Fig. 8 diagrammatically illustrates a modification of the controlcircuits of the embodiment illustrated in Fig. '7 and,

Fig. 9 illustrates a further modification of. the control circuits ofthe embodiment illustrated in Fig. 7.

Referring more particularly to the drawings by characters or reference,reference numeral it designates an alternating current supply lineherein shown as a three phase line for the reason that such type of lineis most frequently utilized in practice. Line ll energizes the primarywinding 62 of a supply transformer having a secondary winding 93comprising a plurality of phase displaced portions which arestarconnected to form a neutral point. The difierent phase portions ofwinding it are severally connected with the anodes it or an electrondischarge device it provided with a cathode H and operable as analternating current rectifier. ation, cathode H is connected with thepositive conductor it of a direct current output line of which thenegative conductor id is connected To obtain such oper till with theneutral point of winding I3. Device it is provided with a plurality ofcontrol electrodes ing 23 at six phase voltages.

one of the star-connected secondary winding portions of a. controltransformer or phase shifter having a secondary winding 23 and having aprimary winding 24 energized from line ii. The neutral point of. winding23 may be connected with conductor I 8 in any one of a number ofdiiferent known ways such as through a battery 26. In the presentembodiment, winding i3 is operable to supply six phase currents anddevice I6 is therefore of the six phase type provided with six anodesand with sixc'ontrol electrodes associated therewith which are energizedfrom wind- Winding l 2 is connected with line H by means of a circuitbreaker 27 which opens under the action of a spring 28 and is maintainedin the closed position thereof against the action of the spring by ,alatch 29. A solenoid 31 is operable to lift latch 3! upon energizationfrom a suitable source such as battery 32 in a manner to be describedhereinafter.

It is generally desired to remove, from the direct current outputvoltage of the rectifier, the alternating current components introducedtherein as a result of the method of connection of the rectifyingequipment. Such components, as is well known, have frequencies which aresix times the frequency of the voltages of line H and all the integermultiples of six times such frequency. Such components are removed bybridging the line by a plurality of resonant filters tuned to thefrequencies of the voltages to be removed and each consisting of areactor 34 in series with a condenser 36. The flow of current in suchfilters is limited by insertion of a series reactor 33 in conductor itor in conductor E9. The voltage of the components filtered out thenappear across the terminals of the reactor. To provide a path for theselective flow of any other voltage component appearing in the directcurrent output circuit and producing a ripple in the output as is wellknown, another resonant filter is connected between conductors l8 and I9preferably on the rectifier side of reactor 33. Such path comprises areactor 37 and a condenser 38 tuned to the frequency of the particularcomponent for which the circuit must provide a path. The flow of currentat such frequency is limited by a resistance 39 and is indicated by anammeter fill preferably provided with a pointer retaining the maximumdeflection given thereto or provided with suitable recording means. Itmay be desired to provide several paths tuned for several frequencies,each path being then provided with the elements recited above for onesuch path. The current flowing through the several tuned paths may beconducted over visible or audible signalling means such as a bell 42and'over the coil of a relay 33. Such relay is preferably of the timedelay type operable to close its contacts 44 upon flow of current ofpredetermined value through the coil thereof for a predetermined lengthof time. Contacts 44 are arranged to complete the circuit of battery 32to solenoid 3| to release latch 29 and cause circuit breaker 2i to openunder the action of spring 28.

The operation of the system will be apparent from a consideration ofFig. 2 in which sine curves 5! to 56, drawn in light lines, representthe positive portions of the voltages of the several portions of windingi3. In the absence of control electrodes in device 16, the directcurrent output voltage appearing between cathode i1 and the neutralpoint of winding l3 would comprise the peaks of successive curves 5| to5B intersecting at points such as points A. Under the action of thecontrol electrodes, each anode will begin to carry current at a latermoment represented by a point such as point B, so that the precedinganode continues to carry current alone over the interval AB. Due to theinductance of the supply transformer, the two anodes carry current inparallel over the following interval BC, after which the second anodecarries current alone. If all anodes and control electrodes areoperating normally, the direct current output voltage will consist ofthe peaks of curves 5| to 56 each extending from a point such as C to apoint such as the following point B and each peak is followed by anindentation over an interval such as BC. Such voltage containsalternating components which have the same values recurring during theperiod of operation of each succeeding anode and accordingly comprise afundamental component having a frequency equal to six times thefrequency of the voltages of line H and, generally, all the harmonics ofsuch component.

For the purpose of illustrating the operation of the system, it will beassumed that the anode receiving voltage 55 fails to carry current forany reason and also that the control electrode associated with the anodereceiving voltage 52 fails to retard the flow of current in such anodepast the point of intersection A of curves 5! and 52. The direct currentoutput voltage of the rectifier is then represented by heavy line 56.Such line shows a pronounced dip recurring once during each cycle of thevoltages of line H at the times when the inoperative anode should becarrying current. Curve 46 therefore presents, in addition to thecomponents mentioned above, a number of alternating components ofpredetermined frequencies and of predetermined magnitudes. The largestof such components is an alternating voltage having the frequency of thevoltages of line H and represented by dotted line all. If one of thefilters 3?, 38 is tuned to the line frequency, a current ofpredetermined value will then flow through such filter, throughindicator ll signal 32 and relay 23. After a predetermined time delay,relay 63 closes contacts M and thereby causes circuit breaker 27 todisconnect device l6 from line i B. An analysis of curve 45 will revealthat such curve will contain alternating components at all the harmonicfrequencies of the frequency of component 37. Such frequencies also havepredetermined magnitudes so that additional filters tuned to suchfrequencies will receive currents of predetermined values.

If more than one anode fails to carry current, some of the voltagecomponents may have values differing from the values obtained when onlyone anode fails, or maybe altogether nonexistent. For example, if twoanodes normally operating in phase opposition simultaneously fail tofunction, no component of line frequency will appear in the outputvoltage and the major component then has a frequency equal to twice theline frequency and is of a predetermined value. An examination of thereadings of indicators 4! during the period of the disturbance will thusreveal the number of anodes which have ceased functioning and also thephase relation between the voltages of such anodes, Failure of onecontrol electrode to control the operation of the associated anodecauses the serration occurring over period AB to be absent from theoutput voltage over the period corresponding to the operation of suchanode, such as the .peak portion of curve 52 in Fig. 2 as indicated atAD. Such failure causes the appearance, in the output voltage, of analternating component at line frequency but of a considerable smallermagnitude than the component caused by failure of one anode to function.Such component will again cause flow of current in filter 3i, 3% tunedto line frequency, the magnitude of such current permitting distinctionbetween the effect of an inoperative control electrode and the effect ofan inoperative anode. When an anode and a control electrode aresimultaneously inoperative, so as to result in an output voltage curvesuch as 3%, the fundamental component due to the failure of the anode ofcurve 55 alone is slightly reduced as a result of the failure of thecontrol electrode and is then represented by curve ll; some of the othercomponents may also be altered, thereby permitting ascertaining of thenature of the trouble within the device it.

Upon occurrence of a short circuit in line i8, it or of a backfire indevice it, the voltage present between line conductors i8, i9 suddenlyfalls to a low value and condensers 36, which during normal operationare charged at the voltage of the line it, it, suddenly dischargethrough indicators All, signal 32, relay (it, conductor it, the point offault or device iii, conductor is, resistances 39 and reactors 3?. Suchflow of discharge current through the coil of relay 63 causes such relayto close contacts Ql, thereby causing operation of circuit brealrer 2iand interruption of the flow of current through device it.

In the embodiment partially illustrated in Fig. 3, it is assumed thatthe supply transformer is provided with a six phase secondary winding tohaving two neutral points connected with conductor it over the usualtype of interphase transformer 5%. Upon failure of one of the anodes orof one oi the control electrodes of device it? to function, voltagecomponents similar to those appearing in the direct current outputcircuit will appear across the terminals oi interphase transformer d9.Filters bl, 8t, indicators ii, signal 52 and relay iii are thereforeconnected across the terminals of inter-phase transformer 69 to receivevoltages appearing at the terminals of such interphase transformerduring abnormal operation only. The alternating current voltagesnormally appearing acrom such terminals will not cause the flowofenyappreciable current through signal 12 and relay it due to thetuning of the filters 3i, to frequencies other than those of such normalvoltages. Battery 26 is herein shown as connected with winding over aresistance 5E3 having the terminals thereof connected with contacts idof battery During normal operation, the current drawn by the controlelectrodes produces, in resistance 5d, a small ohmic drop which is takeninto consideration when adjusting phase shifter 23, 24!. Upon closure ofcontacts (it of relay Q3, battery 32 impresses on all control electrodesan additional negative voltage suficient for continuously maintainingthe control electrodes at a negative potential with respect to cathodeil, thereby causing interruption of a current flowing through device it.As in the embodiment illustrated in Fig. 1, relay is is provided with atime delay device so as to preclude operation of such relay upontemporary failure of functioning of one of the electrodes of device it,as such temporary faulty operation would not cause deterioration of thedevice it. Such time delay device also prevents relay 33 from closingupon occurrence of transient surges in the direct current circuit whichsurges may contain comaraaecc which one of the filters 311, 3B, 39 iswhich may therefore cause the flow ponents to tuned and of a transientcurrent in the coil of relay 53.

In either case signal 52 will operate and one or more of indicators llwill record the transient iiow of current so that the attendant may becognizant of such transient condition although the device was notdisconnected from the supply line. When current flowing through device56 has been interrupted, current no longer flows in the coil of relay 33and contacts it are thereafter maintained closed by a holding coil 55provided on relay 63. A switch ht permits resetting relay 63 bymomentarily opening the circuit of battery 82.

It will be understood that, by a suitable adjustmerit of phase shifter23, 2d, device it may be operable to function as an inverter forconverting direct current from line it, it into alternating currentsupplied to line i 0, without thereby afiecting the operation or theusefulness of the system described.

In the embodiment illustrated in Fig. 4, the operation of relay S3 isshown as being responsive to the flow of current components ofpredetermined frequencies in the neutral connection of winding 23resulting from the failure of one of the control electrodes ii tofunction. To obtain such efiect suitable impedance means such as aresistance 51! and a reactor 58 are inserted between the neutral pointof winding 23 and battery 25 and the voltage drop across resistance 5?and reactor 58 is impressed on a plurality of filters 3i, indicators ll,signal 32 and the coil of relay 13. As is well known, control electrodes2i function in a manner similar to that of anodes to so that the currentin the neutral lead of winding 23 normally has a wave shape resemblingthe wave shape of the output direct current of device [16. Such currenttherefore normally contains harmonic components of predeterminedfrequenor to which filters 3i, should not be tuned. Failure of one ofthe control electrodes to function causes the appearance, in the currentof the neutral lead or" the control transformer, of alternatingcomponents of predetermined frequencies and magnitudes which cause flowof current through filters 3?, 38, indicators 8 5, signal G2 and coil ofrelay 13 as set forth in relation to the embodiment illustrated in Fig.i.

If the rectifying system utilizing device it supplies current to a linealso receiving current from other converting equipment such as rotaryconverters, the voltage of the direct current line is maintained at asubstantially uniform value by such converters. Reactor 33 and filters36, 36

- may then be omitted, and the alternating voltage components appearingin the embodiment illustrated in Fig. 1 then no longer appear in therectifier output voltage. It is then necessary to utilize thealternating components of predetermined frequencies appearing in thecurrent delivered by device it, and which were not utilizedin thepreceding embodiments. As shown in Fig. 5, such current components maybe utilized in a manner similar to that illustrated in Fig. 4 byinserting, in one of the direct current conductors such as it, suitableimpedance means such as resistance 59 and reactor 68. The voltage dropacross such impedance means is then impressed on the same circuits as inthe embodiment illustrated in Fig.

4 in which filters 31, 38 are tuned to frequencies omitted and thecontrol electrodes receive a negative direct current voltage componentfrom a voltage divider comprising rheostats 88 and 89 connected inseries between conductors I8 and I9. Automatic control of energizationof the control electrodes to maintain the current within device I6 at aconstant value is obtained by constructing rheostat 89 as part of aregulator such as a regulator 9I of the rocking contact type. Regulator9| includes a stator core 92 energized by means of a winding 93, and anarmature 94 rotat'able'on a spindle 96 and carrying a winding Cal 91connected in series with winding93. Windings 93 and 91 are energized inresponse to the variations of the current in conductor I8 by means of ashunt 99 over a regulating rheostat IOI and a resistance I02. The torqueof spindle 96 resulting from such current flow is opposed by a spring 98or by a combination of springs having a constant torque over the rangeof motion of the regulator. Spindle 96 carries a hub I03 serving as afulcrum for a rocking sector I04 which moves either in direct contactwith resistance 89 or over a separate contact path comprising aplurality of conductive segments (not shown) severally connected withthe portions of resistance 89. Sector I04 is connected with the neutralpoint of winding 23, so that movement of such sector causes theconnection of such neutral point with portions at difierent potentialsof resistance 89. 1

When the current flowing through the device is lower than desired,spring 98 rotates spindle 96 and sector I04, thereby causing the pointof contact of sector I04 with resistance 89 to move toward conductor I8. The negative voltage equal to the voltage drop in the portion ofresistance 89 between the point of contact and conductor I8 decreases,thus causing the control electrodes to become positive with respect tocathode II at an earlier moment of the voltage cycle of line II and tothereby cause a large flow of current through device I6. When thecurrent through the device becomes too large; armature 94 rotatesspindle .96 against the action of spring 98 to produce a currentreduction by a process opposite to that above described, the value ofcurrent thus automatically maintained may be adjusted by means ofrheostatIOI.

In the present embodiment, when the relay 43 closes contacts 44,resistance I02 is short cir-- cuited, thereby adjusting the setting ofregulator 9| in such a manner as to cause such regulator to maintain theflow of current within device I6 at a lower value, which will not causethe anodes remaining in operation tobecome overloaded.

In the embodiment illustrated in Fig. 6, winding 48 is assumed to beutilized in conjunction with an electron discharge device 62 providedwith I2 anodes. The current from each portion of winding 48 is thenpreferably conducted to two of the anodes of device 62 and additionalmeans must be provided to causea substantially equal division of currentbetween such anodes. Such means preferably consist of a six phaseparalleling transformer having a primary winding 63 and a three phasesecondary winding. 64 and a second similar paralleling transformerhaving a primary winding 66 and-a secondary winding 6?. As is wellknown, the division of current between the anodes connected with eachportion of winding 63 and the anodes connected with each por tion ofwinding 66 is effected by the flow of three phase currents betweenwindings 64 and 61. During normal operation, if the neutral points ofwindings 64 and 61 are conductively connected, such connection will notreceive any current. The coil of relay 43 and signal 42 may therefore beinserted in such connection and will not receive any current duringnormal operation of device 62. If one of the anodes of device 62 failsto carry current the currents circulating between windings 64 and 6!will no longer be balanced so that a residual current will flow betweenthe neutral points of such windings over the coil of relay 43 and signal42.

In the present embodiment, relay 43 is assumed to have contacts 44thereof arranged to connect battery 32 with the trip coil 40 of acircuit breaker 45 inserted in conductor I8. Upon closure of contacts44, circuit breaker 45 opens and disconnects device 62 from the outputline, so that the device no longer carries current as if such devicewere disconnected from the supply line in the manner illustrated inFig. 1. The circuit of trip coil 40 is completed over the contacts of arelay I06 energized in response to the flow of current in device 62 bymeans of a shunt I0I. The circuit of trip coil 40 is then not completedand circuit breaker 45 does not open if thecurrent in device I6 has avalue which will not cause the anodes remaining in operation to becomeoverloaded. It will be understood also, that, in the present embodiment,relay 43 may be utilized for controlling the opening of a circuitbreaker in the supply circuit of the device as previously illustratedand described.

In the embodiment illustrated in Fig. 7, winding 48 is assumed to supplycurrent to an electron discharge device 68 provided with eighteenanodes. Each portion of winding 48 is then preferably connected tosupply current to three anodes of device 68 which anodes then operate inparallel; the equal division of current between the parallel anodes isobtained by means of three single phase paralleling transformers eachhaving a double primary winding 69;-I2,or I4 anda secondary winding II,I3, or I6. During normal operation, the currents in windings II, I3, andI6 constitute a balanced three phase system of curv rents so that thethree windings may be connected in parallel with each other to a circuitcomprising the coil of relay 43 and signal 42. During such normaloperation there will not be any flow "of residual current through coilof relay 43 and signal 42. Upon failure of one of the anodes of device68 to function the currents ofwindings II, I3, 16 no longer constitute abalanced three phase system of current and a residual current will flowthrough the coil of relay 43 and signal 42 to give a, signal and causecircuit breaker 21 to disconnect winding I2 from line II.

It may be desired not to connect windings II, I3, I6 in a conductivemanner so as to relieve the stress on the insulation between the primaryand secondary windings of the several paralleling transformers resultingfrom such conductive connection. Windings II, I3, and I6 may then beconnected with the circuit of the coil of relay 43 and signal 42 over a,plurality of current transformers 77, I8, and 19 having theirsecondaries connected in parallel as shown in Fig. 8.

Relay 43 may also be provided with a plurality of operating coils 84, 85, 86 as shown in Fig. 9, which are severally connected with windingsII, 73, and 16 and which act on a single armature 81. In this manner therelay will close contacts 44 only upon occurrence of an unbalancebetween the currents flowing in coils 84, 85, and 86. In the presentembodiment, signal 42 is preferably connected in parallel with solenoid3i and is operated from battery 32 upon closure of contactstt.

Features specific to certain of the herein disclosed embodiments ofthepresent invention are claimed in a divisional application filedAugust 13, 1937 and having Serial No. 158,843; and although but a fewembodiments thereof have been illustrated and described, it will beapparent to those skilled in the art that various changes, andmodifications may be made therein without,

departing from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent:

1. In a protective system for electron discharge devices, an alternatingcurrent supply nected with said device, means for interrupting flow ofelectric current through said device, and means receiving and operatingin response to harmonic current components appearing upon abnormaloperation of said device, said means causing operation of the first saidmeans.

3. In a protective system for electron discharge devices, a supply line,an electron discharge device connected with said line, an output lineconnected with said device, means for interrupt ing flow of electriccurrentthrough said device, and means receiving and operating inresponse to harmonic current components of predeter-- mined frequenciesappearing in the system only upon abnormal operation of said device,said means causing operation of the first said means.

4. In a protective system for electron discharge devices, a supply line,an .electron discharge device connected with said line, an output lineconnected with said device, means for interrupting flow of electriccurrent through said device, and means receiving and operating inresponse to alternating current components of predetermined frequenciesappearing in one of said lines only upon abnormal operation of saiddevice to cause operation of said interrupting means.

5. In a control system for electron discharge devices, a source-ofalternating current, an electron discharge device connected with saidsource, circuits connected with said device and receiving currents ofpredetermined frequencies relative to the frequency of said source onlyupon abnormal operation of said device, means for interrupting the flowof current through said device, and means operable upon energization ofany of said circuits to cause operation of said interrupting means. I

6. In a protective system for electron discharge devices, a supply line,an electron discharge device connected With said line, an output lineconnected with said device, means for interrupting flow of electriccurrent through said device, and means receiving and operating inresponse to harmonic current components appearing in said output lineupon abnormal operation-of said device, said means causing operation ofthe first said means.

- arcaese 7. ma control system for electron discharge devices, analternating current line, a transformer connected with said alternatingcurrent line, an electron discharge device connected with saidtransformer, a direct current line connected 5 with said device, acircuit breaker for interrupting the flow of current through saiddevice, circuits tuned to predetermined frequencies appearing in saiddirect current line only upon abnormal operation of said device, andmeans operable upon energization of any of said circuits to causeopening of said circuit breaker.

8. In combination with direct and alternating current circuits, anelectron discharge device interconnecting said circuits comprising aplurality of electrodes forming asymmetric conductors for transformingcurrent received from one of said circuits and the supply thereof to theother of said circuits, and a plurality of control electrodes severallyassociated with said conductors, of means including a regulatorconnected with and continuously applying to said control electrodespotential of such sign and magnitude as to prevent initiation of flow ofcurrent through said device by way of said conductors, means havingconnections with and periodically applying potential to said controlelectrodes of such sign and magnitude and during such recurring periodsas to permit and control the moments of initiation of flow of currentsequentially through said conductors, the said regulator havingconnections with and being responsive to the magnitude of flow ofcurrent in said other of said circuits during normal operation of saiddevice to vary within predetermined limits the magnitude of'saidpotential continuously applied to said control electrodes, and meansreceiving current from the said other of said circuits onlyduringabnormal operation of said device for causing the said regulator to-varythe magnitude of said potential continuously applied to said controlelectrode beyond said predetermined limits.

9. The combination of a supply circuit, a distribution circuit, electrondischarge means interconnecting said circuits and comprising a pluralityof asymmetric conductors for transforming currentreceived from one ofsaid circuits and the supply thereof to the other of said circuits,means operable to limit the said current to values within predeterminedmaximum and minimum limits during normal operation of the first saidmeans, and means operable responsive to abnormal operation of the firstsaid means for affecting the operation of the second said means in suchsense as to thereby limit said current to a value below said minimumlimit.

10. The combination of a supply circuit, a distribution circuit,electron discharge means interconnecting said circuits and comprising anasymmetric conductor for transforming current received from one of saidcircuits and the supply thereof to the other of said circuits, meanscomprising an electrode associated with said conductor for controllingthe operation thereof, means operable responsive to operation of thefirst said means during normal operation thereof for affecting theoperation of the second said means in such sense as" to thereby limitsaid current to values within predetermined maximum and minimum limitsand operable responsive toabnormal operation of the first said means foraffecting the operation of the second said means in such, sense as tothereby limit said current to a value below said minimum limit.

11. The combination of a supplycircuit, a (115- 75 during normal2,123,859 tribution circuit, electron discharge means inter-' connectingsaid circuits and comprising a plurality of asymmetric conductors fortransforming current received from one of said circuits and the supplythereof to the other of said circuits, means operable during normaloperation of the first said means for regulating the value of saidtransformed current, and means operable responsive to abnormal operationof the first said means for affecting the operation of the second saidmeans in such sense as to modify the said regulating action thereof.

12. The combination of a supply circuit, a distribution circuit,electron discharge means interconnecting said circuits and comprising anasymmetric conductor for transforming current received from one of saidcircuits and the supply thereof to the other of said circuits, meansoperable responsive to operation of the first said means operationthereof for regulating the value of said transformed current, and meansoperable responsive to abnormal operation of the first said means foraffecting the operation of the second said meansin such sense as tomodify the said regulating action thereof.

13. The combination of an alternating current supply circuit, a directcurrent output circuit, electron discharge means interconnecting saidcircuits and comprising an asymmetric conductor for transforming currentreceived from the said supply circuit and the supply thereof to the saidoutput circuit, means operable during normal operation of the first saidmeans for regulating the value of said transformed current, and meansoperable responsive to alternating current components appearing in thesaid output circuit upon abnormal operation of the first said means foraffecting the operation of the second said means in such sense as tomodify the said regulating action thereof.

14. The combination of an alternating current supply circuit, a directcurrent output circuit,

circuits and comprising an asymmetric conductor for transforming currentreceived from said supply circuit and the supply thereof to the saidoutput circuit, means operable during normal operation of the first saidmeans for regulating the value of said transformed current, and meansconnected with said output circuit and receiving alternating currentcomponents of predetermined frequencies relative to the voltagefrequency of electron discharge means interconnecting said said supplycircuit upon abnormal operation of the first said means for affectingthe operation of the second said means in such sense as to therebymodify the said regulating action thereof.

15. The combination of an alternating current supply circuit, a directcurrent output circuit, electron discharge means interconnecting saidcircuits and comprising an asymmetric conductor for transforming currentreceived from said supply circuit and the supply thereof to said outputcircuit, means operable to limit the said current to values withinpredetermined maximum and minimum limits during normal operation of thefirst said means, and means connected with said output circuit andreceiving alternating current components of predetermined frequenciesrelative to the voltage frequency of said supply circuit upon abnormaloperation of the first said means for afiecting the operation of thesecond said means in such sense as to thereby limit the said current toa value below said minimmu limit.

HAROLD WINOGRAD.

